Briefly, the present invention relates to a method and apparatus for sputtering of a thin film of a compound onto a substrate workpiece by means of cathodic, magnetron sputtering.
Application of metals and metallic compounds by use of a reactive deposition process is known and is the subject, for example, of U.S. Pat. No. 4,428,811, "Rapid Rate Reactive Sputtering Of A Group IVB Metal" issued Jan. 31, 1984, incorporated herewith by reference. U.S. Pat. No. 4,428,811 discloses a method and apparatus for rapid rate deposition of metallic compounds such as titanium nitride onto a substrate in a vacuum chamber. In the process, the chamber is filled with inert gas that is ionized and bombards the metal target within the chamber to initiate the sputtering process. A substrate is positioned within the chamber for coating, and a second reactive gas is fed into the chamber at a measured rate to combine at the substrate with the atomized metal from the target to form the coating. Control systems for such sputtering operations are also disclosed in the aforesaid patent.
Over the years, the technology associated with sputtering processes has been improved so that additional compounds and materials can be applied to a substrate by. A series of papers by the co-inventor reflect research in this area including the following:
1. "High Rate Reactive Sputtering Process Control," published in Surface and Coatings Technology, 1987;
2. "The Effect of Target Power on the Nitrogen Partial Pressure Level and Hardness of Reactively Sputtered Titanium Nitride Coatings," published in Thin Solid Films, 1989;
3. "Advances in Partial-Pressure Control Applied to Reactive Sputtering," published in Surface and Coatings Technology, 1989;
4. "The Effect of N.sub.2 Partial Pressure, Deposition Rate and Substrate Bias Potential on the Hardness and Texture of Reactively Sputtered TiN Coatings," published in Surface and Coatings Technology, 1989;
5. "Deposition and Properties of Polycrystalline TiN/NbN Superlattice Coatings," published in J. Vac. Sci. Technol. A 10/4, July/August 1992; and
6. "Control of a Reactive Sputtering Process for Large Systems," a paper presented at the Society of Vacuum Coaters, 36th Annual Technical Conference, Dallas, Tex., Apr. 30, 1993.
The text of these publications is incorporated herewith by reference.
The energy source which effects the ionization of the inert gas in a sputtering system has evolved over time so that now pulsed, direct current electrical power is known to be a preferred energy source to the target material. Publications relating to this technique and technology include the following:
7. "Mechanisms of Voltage Controlled, Reactive, Planar Magnetron Sputtering of Al in Ar/N.sub.2 and Ar/O.sub.2 Atmospheres," published in J. Vac. Sci. Technol. A 2(3), July-September 1984; and
8. "Pulsed Magnetron Sputter Technology," published in Surface and Coatings Technology, 1993.
These publications are incorporated herewith by reference.
Sputtering techniques for the application of pure metals are fairly well refined and effective. Additionally, sputtering techniques for conductive or non-insulating compounds have been somewhat successful utilizing the techniques described in the aforesaid publications. However, certain materials, which provide an insulating, hard coating upon a substrate are difficult to apply as a film or may not be efficiently applied using such sputtering techniques. Aluminum oxide, for example, has heretofore been applied by sputtering techniques to a substrate at only a small fraction of the rate and efficiency of the application associated with the pure aluminum metal. Thus, low deposition rates of insulating or non-conductive metal compounds have continued to pose a challenge. Publications that reflect research regarding the sputtering of such compounds include the following, which are incorporated herewith by reference:
9. "Aspects and Results of Long-Term Stable Deposition of Al.sub.2 O.sub.2 with High Rate Pulsed Reactive Magnetron Sputtering," published in Surface and Coatings Technology, 1993;
10. "Reactive Direct Current Magnetron Sputtering of Aluminum Oxide Coatings," J. Vac. Sci. Technol. A 13(3), May/June 1995; and
11. "Reactive DC Magnetron Sputtering of the Oxides of Ti, Zr, and Hf," presented at the International Conference on Metallurgical Coatings and Thin Films, Town and Country Hotel, San Diego, Calif., Apr. 24-28, 1995, and accepted for publication in Surface and Coatings Technology.
In sum, there has remained a need to provide an improved method and apparatus for the deposition of metallic, insulating compounds such as aluminum oxide, on a substrate using sputtering techniques.